For safe operation of an aircraft, the Weight of the aircraft must be determined prior to take-off, Airlines (also referred to as: FAA/Part 121 “Air Carriers”) have strict departure schedules which are maintained to maximize aircraft utilization each day. Today's airline operations typically do not place fully loaded aircraft upon scales as a means to measure the aircraft weight, and the distribution of that weight commonly referred to as the aircraft Center of Gravity (“CG”): prior to an aircraft's departure (“dispatch”) from an airport gate.
On any single day within the United States, airlines average 28,537 departures; where each of these air carriers must determine the weight and CG for each aircraft prior to departure, United States population has progressively become heavier over the years; thereby the individual weight of each passenger on these aircraft has become heavier. Airlines around the world operate on a very strict time-schedules, where even a short departure delay occurring early in the day can have a ripple effect and create scheduling problems throughout the airline's remaining flight schedule. Aircraft load planning is a crucial part of keeping an airline operating on schedule. A scheduled aircraft departure will commence its load planning process up to one year prior to the actual flight. Airlines do not offer ticket sales for a flight more than twelve months prior to the flight. As each ticket for a scheduled flight is purchased, the average passenger and average checked bag weights are assigned into a computer program, continually updating throughout the year the planned load for that flight. Aircraft have a Maximum Take-Off. Weight “MTOW” limitation. Airline load planning procedures use assumptions as to the weight of passengers and baggage loaded onto the aircraft, to stay below the aircraft MTOW limitation.
In the United States of America, aircraft weights are limited by Federal Aviation Administration “FAA” regulation. The FAA is the Regulatory Authority which regulates the design, development, manufacture, modification and operation of all aircraft operated within the United States, and will be referenced along with the term “Regulatory Authority” to indicate both the FAA and/or any governmental organization (or designated entity) charged with the responsibility for either initial certification of aircraft or modifications to the certification of aircraft. Examples of other Regulatory Authorities would include: European Aviation Safety Agency “EASA”, within most European countries; Transport Canada, Civil Aviation Directorate “TCCA”, in Canada; Agéncia Nacional de Aviação Civil “ANAC” in Brazil; or other such respective Regulatory Authority within other such respective countries.
FAA Regulations (provided in the Code of Federal Regulations) are the governmental regulations which detail the requirements necessary for an aircraft to receive certification by the Regulatory Authority within the United States. These would be equivalent to such regulations within the Joint. Aviation Regulations “JARs” which are used in many European countries.
Title 14 of the Code of Federal Regulations, Part 25 refers to regulations which control the certification of Air Transport Category aircraft (“Part 25 aircraft”) Part 25 aircraft include most of the commercial passenger aircraft in use today. For example, Part 25 aircraft includes Boeing, model numbers 737, 747, 757, 767, 777; Airbus A300, A310, A320, A330, A340, etc. The methods described herein provide the justification basis needed for a Regulatory Authority to allow increases to the aircraft weight limitations and expansion of the aircraft CG limitations, in particular for airlines which do not provide assigned seating for their passengers. The FAA regulations allow for control mechanisms to assure Part 121 air carriers manage aircraft loading procedures to confirm at the completion of the loading process that the aircraft load remains within the aircraft's certified forward and aft CG limits.
In particular:                Title 14—Code of Federal Regulations:        Part 121—695, subparagraph (d)        § 121.695 Load Manifest: All Certificate Holders                    The load manifest must contain the following information concerning the loading of the airplane at takeoff time:            (a) The weight of the aircraft, fuel and oil, cargo and baggage, passengers and crewmembers.            (b) The maximum allowable weight for that flight that must not exceed the least of the following weights:                            (1) Maximum allowable takeoff weight for the runway intended to he used (including corrections for altitude and gradient, and wind and temperature conditions existing at the takeoff time).                (2) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with applicable en route performance limitations.                (3) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with the maximum authorized design landing weight limitations on arrival at the destination airport.                (4) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with landing distance limitations on arrival at the destination and alternate airports.                                    (c) The total weight computed under approved procedures.            (d) Evidence that the aircraft is loaded according to an approved schedule that insures that the center of gravity is within approved limits.            (e) Names of passengers, unless such information is maintained by other means by the certificate holder.                        
If an airline is found to be operating a Regulated aircraft with weights in excess of the aircraft's certified weight limitations, that airline is subject to Federal penalties and fines. It is a violation of Federal Law to knowingly operate an aircraft, when the aircraft weight has exceeded any of the Original Equipment Manufacturer's (“OEM's”) certified weight limitations.
All air carriers must have FAA approved procedures in place (“an approved schedule”), in which the air carrier will follow such procedures to insure each time an aircraft is loaded, the load will be distributed in a manner that the aircraft CG will remain within the forward and aft CG limitations. The FAA and the specific air carrier develop these procedures, which are often referred to as “loading laws,” and when implemented define how the aircraft is loaded. An accurate determination of the total passenger weight portion of a flight could most readily be accomplished by having a scale located at the entrance to the aircraft door, by which all weight that enters the aircraft would be measured. Though this solution sounds simple, having the measured weight of the passengers and their carry-on items would cause substantial disruption in an airline's daily flight, schedule if the aircraft in which the planned load where to have all of the loaded weights measured; to only at moments before the aircraft is scheduled to depart finds the aircraft weight now exceeds the MTOW limitations. An aircraft delay would result and many dissatisfied passengers would be required to be removed from their planned flight.
The FAA has established guidelines through the issuance of an Advisory Circular AC No: 120-27E, dated Jun. 10, 2005, “Aircraft Weight And Balance Control”; in which an airline is allowed to determine aircraft weight through the adoption of a “weight and balance control program” for aircraft operated under Title 14 of the Code of Federal Regulations (14CFR) part 91, subparts 121, 125 and 135. Part 121 deals with scheduled air carrier operations, including airlines such as American, Delta, United and Southwest.
The aircraft operator will use approved loading schedules to document compliance with the certificated aircraft weight limitations contained in the aircraft manufacturer's Aircraft Flight Manual (AFM), for the compiling and summing of the weights of various aircraft equipment, fuel and payload weights, along with the AC120-27E weight designations for passengers and baggage. These types of loading schedules are commonly referred to as the Load Build-UP Method (LBUM).
The aircraft LBUM weight determinations are “computed” with the use of guidance from AC120-27E and considered by the FAA as being 100% accurate, The FAA accepts an aircraft weight which is established under an approved weight and balance control program, using the guidance from AC120-27E as to having zero error in the total aircraft weight; not even one pound of error.
AC120-27E defines approved methods to determine the aircraft weight using “weight assumptions” which are independent of any requirement to use scales to measure of the aircraft total weight at dispatch. The fully loaded weight of the aircraft is established through a process of compiling the weights of various payload items based upon FAA approved “designated” average weights, for the varying elements such as passengers, carry-on baggage, checked baggage, crew weight, cargo weight and the weight of fuel loaded; onto a previously measured empty aircraft weight. AC120-27E designates for large aircraft (being aircraft certified to carry more than 70 passengers) approved weight assumption/designation for passengers and baggage as:
passenger weight - May-October190.0lb.passenger weight - November-April195.0lb.checked bag weight28.9lb.checked as “heavy” bag weight58.7lb.
Historical weather patterns regarding wind velocity and direction, combined, with anticipated storm events along scheduled airline routes are also considered when planning the amount of fuel to be consumed during the flight. On the actual day of a flight, typically two hours prior to the departure of that flight, the airline's automated load planning program will transfer this particular flight plan to the desktop computer display of one of the airline's Flight Dispatchers. It is the responsibility of the Flight Dispatcher to then monitor the planned load of this flight as passengers check-in and board the aircraft. The number of passengers and checked bags are input to the load-planning program. Typically this process goes without interruption and the aircraft will dispatch on schedule, as planned. As the aircraft's door closes and the load-plan is dosed-out by the Flight Dispatcher, the aircraft weight associated with the “planned load” will always match, the aircraft weight associated with the “departure load” as submitted to the FAA; because both are based on the same collection of weight assumptions used in determining the LBUM. Use of an alternate means to physically measure the total aircraft weight, just as the aircraft door doses, and the possibility of the measured aircraft weight not matching the calculated weight of the LBUM, would have the airline facing a potential departure delay, to resolve any difference in the two separate but parallel aircraft weight determinations. This potential for delay in the flight departure on as many as 2,500 daily flights for a single airline, results in the various airlines not willing to take the risk of hundreds of flight delays each day. Many if not most airlines currently dispatch their aircraft under FAA. approved LBUM procedures; a method which helps to keep the airlines running on schedule. This also creates an incentive for airlines to continue to use the FAA approved assumed weights, irregardless to whether the assumed aircraft weight determinations are accurate.
Some airlines offer “assigned seating” within the cabin compartment for their passengers. This process not only allows the passenger the assurance that they will have the seat of their choosing, but also allows the airline load planners the knowledge of the exact location within the cabin as to where the weight associated with that passenger and their carry-on items is located. Airlines which do not offer the option of pre-assigned seating must entrust their load planning departments to determine aircraft CG, lacking the knowledge of where the passenger weights will be located within the aircraft cabin. If an aircraft operated with an open-seating policy has in excess of 80% of the seats filled with passengers, the weight distribution shall be assumed equally distributed throughout the cabin. If the same aircraft departs with only 30% of the seats occupied, the airline, has no assurance as to where the weight is located throughout the cabin.
Herein are two examples to better illustrate §121.695 subparagraph (d) mentioned above. The Boeing 737-800 aircraft has a seating configuration for 174 passengers, in which only 52 passengers (30%) were boarded onto the flight, and will be used in the following examples:                Example #1—an air carrier which operates with an “assigned seating” policy can position the 52 passengers (being just 30% of total) and their associate weight, distributed evenly throughout the aircraft cabin; thus assuring the cabin load remains within the forward and aft CG limits. With each passengers assigned a specific seat located within a specific row number, the airline can plan the aircraft load with confidence that the aircraft will be loaded within the aircraft CG limitations.        Example #2—an airline which has an “open seating” policy, there is a possibility that the 52 passengers may all select a seat within the forward section of the aircraft, in order to be seated forward of the aircraft wing and the engine noise associated with those seats located aft of the wing; and to further be able to quickly exit the aircraft upon arrival at their destination. In this scenario where all 52 passengers are seated within the forward ⅓ section of the aircraft, the aircraft CG has the potential of being positioned beyond the certified forward CG limit of tine aircraft.        
To insure the aircraft CG, as loaded in Example #2, remains within the CG limitations, the FAA will place additional operational restrictions, often called “curtailments” to the extreme forward and extreme aft sections of the manufacture's defined CG envelope. The airline which operates with these curtailments must take actions to insure the aircraft remains within these Regulatory Authority imposed “operationally curtailed” CG limitations through methods such as blocking-off the some of the forward and aft rows of the aircraft seating, or to possibly add temporary “ballast” (heavy bags filled with lead pellets) into the forward or aft cargo compartments of the aircraft, to assure these partially loaded flights will remain within the “operationally curtailed” CG limitations. A full description of these curtailments along with the new methods of this invention for relief of these curtailments will be explained later.
The positioning of passenger weight is important to the aircraft flight planning process. The Boeing 737-800 aircraft has an overall length of 129 feet 6 inches, from nose to tail. Considering an airline operation which has the full use of the CG limitations with no curtailments, at the reduced take-off weight of 150,820 lbs., the airline's load planner has but only 42 inches (see HO I.) to position the cabin and cargo compartment loading, from the originally aircraft's certified CG limitations. If the load planner fails to stay within the forward end of this 42-inch window, the CG 27 will be too far forward, where the aircraft may fail to properly rotate for take-off and a subsequent rejected take-off could over-run the length of the airport runway. If the load planner fails to stay within the aft end of the 42-inch window, the CG will be too far aft, where the aircraft may over-rotate at take-off resulting in a tail-strike, or transition into a stall where the aircraft could possibly crash.
Accurate determination of aircraft take-off weight is an important part of load planning in that it riot only adds to the safety of each flight it also is an important consideration regarding the overall life, limitation of the aircraft. The aircraft weight can be incorrect by as much as 2,000+ pounds and a “properly balanced” aircraft will still take-off, using and extra 100 feet of the available 10,000 feet of runway. The additional weight could come from a variety of possible mis-calculations, but typically will not affect the aircraft take-off.
An aircraft is typically supported by plural and in most cases three pressurized landing gear struts. The three landing gears are comprised of two identical main landing gear struts, which absorb landing loads, and a single nose landing gear strut used to balance and steer the aircraft as the aircraft taxis on the ground. Designs of landing gear incorporate moving components which absorb the impact force of landing. Moving components of an aircraft, landing gear shook absorber are commonly vertical telescopic elements. The telescopic shock absorber of landing gear comprise internal fluids, both hydraulic fluid and compressed nitrogen gas, and function to absorb the vertical descent threes generated when the aircraft lands. While the aircraft is resting on the ground, the aircraft is “balanced” upon three pockets on compressed gas within the landing gear struts.
Monitoring the distribution and subsequent re-distribution of aircraft loads can be identified by measuring changes in the three landing gear strut internal pressures, which will in turn identify the aircraft CG. The implementation of changes to aircraft loading procedures for both the assumptions as to the weight of items loaded onto the aircraft, as well as the location within the aircraft the weights are placed, further combined with strict auditing procedures to identify non-recognized weight errors associated with the weight assumptions, create the justification basis to allow aircraft weight and CG limitations to be modified.
In spite of numerous variations in prior art for aircraft on-board weight and balance systems (“OBWBS”), no U.S. airlines currently use OBWBS in their daily operations, but instead all major airlines typically use the LBUM to determine aircraft weight.
This invention offers new methods with apparatus to “periodically” measure aircraft weight, in support of re-defined load planning procedures and records-keeping, to create the justification basis for increases in the aircraft weight limitations and an easing of operational CG curtailments for Regulated aircraft.
Additionally, the creation of the justification basis for an increase to weight limitations for Regulated aircraft, to a higher weight limitation equivalent to the amount of the currently allowed statistical error in weight assumptions of the LBUM shall be fully described in the new methods of this invention for relief to weight limitations and CG curtailments and will be explained fully throughout the Figures and Descriptions herein.
It should be noted that the Regulatory Authorities have various practices to provide relief or modification to the regulatory requirements, such as:                Equivalent Level of Safety        Special Condition        ExemptionThis relief is normally granted by the Regulatory Authority, after demonstration and/or analysis of an alternate means of compliance, which verifies compliance with the intent of the regulation, without showing literal compliance to the regulation.        
Another aspect of this invention are methods by which Part 121 air carrier operations utilizing “random open seating” polices are justified in receiving relief from operational CG curtailments caused by aircraft loading assumptions, to an equivalent of the broader CG curtailments of air carrier operations using “assigned seating” policies, whereby the operational CG limitations of a Part 25 aircraft may be increased and acknowledged by aviation Regulatory Authorities. One of the methods of this invention involves analysis of periodically obtained, weight and/or CG data from daily airline operations, combined with development and implementation of set of new daily operational requirements for the Part 25 aircraft; thus providing by either: a demonstration and/or analysis to substantiate, a finding of an “Equivalent Level, of Safety” and/or “Special Condition”.
The FAA defines an Equivalent Level of Safety (ELOS) as follows:                “Equivalent level of safety findings are made when literal compliance with a certification regulation cannot be shown and compensating factors exist which can be shown to provide an equivalent level of safety.”                    {http://rg1. faa.gov/Regulatory_and_Guidance_Library/rgELOS.nsf/}.                        
The FAA issues a finding of ELOS during the process of certification, whether that be the initial certification of an aircraft, certifications of derivative aircraft the manufacturer may develop or when issuing a Supplemental Type Certificate for modifications to an aircraft type, developed by entities other than the manufacturer.
In the case of existing air carrier operations die “literal compliance” with an accurate determination of aircraft weight and CG, which cannot be shown, however the “compensating factors” which exist in this new invention to substantiate the ELOS finding include:                The incorporation of apparatus and methods to measure, periodically record and display (or generate alerts) when defined weight and/or CG thresholds are exceeded and, one or more of the following additional elements:                    The Approved Flight Manual for the aircraft contains specific operationally imposed weight and CG limits with which the aircraft must apply and provides fur compliance with the traditional LBUM in determining aircraft total weight, if the ability of the system's periodic sampling of weight and CG becomes inoperative;            Apparatus and methods for periodically recording aircraft weight and/or CG for a specific sample size of aircraft dispatches in support of a trend monitoring system to monitor the “experienced” aircraft loading; as compared to both the specific load manifest of the periodically weighed aircraft and that of the loading pattern trends of. the airline's full fleet of aircraft;            Alerting to the flight deck crew if the real-time sampled weight and/or CG has, exceeded one or more pre-defined thresholds.                        
The FAA defines Special Condition as follows:                “A Special Condition is a rulemaking action that is specific to an aircraft type and often concerns the use of new technology that the Code of Federal Regulations does not yet address. Special Conditions are an integral part of the Certification Basis and give the manufacturer permission to build the aircraft, engine or propeller with additional capabilities not referred to in the regulations.”                    {http://rg1.faa.gov/Regulatory_and_Guidance_Library/rgSC.nsf/}.                        
A requirement for periodic sampling of physically measured aircraft dispatch weight and CG is not referred to in the regulations; therefore a pathway for Special Condition is created.
A Regulatory Authority may wish to approve such installation, use and regulatory relief from such a System, by the issuance of a Special Condition as an alternative to the granting approval established by an ELOS, based upon no regulator requirement or definition of a System which, measures aircraft take-off weight and CG. Regardless of the regulatory approval path used, the System attributes would be the same.
One of the methods of this invention comprises analysis of “statistically generated” random passenger weights with application of potential non-recognized errors in both the average passenger and average baggage weight data, to be further compared to the distinct 190 lb. weight designation to an additionally assumed 50% male/50% female passenger profile boarding onto the aircraft; further combined with development and implementation of set of new daily operational requirements for the Part 25 aircraft; thus providing by either; a demonstration and/or analysis to substantiate, a finding of an “Equivalent Level of Safety” and/or “Special Condition”.
Though the FAA may continue to assume aircraft weight determinations, as computed within the guidance of AC120-27E, to have zero errors in the aircraft weigh. determination; a statistical evaluation and review of the FAA approved methods finds significant errors in the LBUM weights which remain un-recognized by the FAA. It will be the identification and quantification of these un-recognized weight errors and the ability to absorb these errors into and with the physical measurement of the aircraft weight, that will create a satisfactory justification basis for Regulatory Authorities to allow regulated aircraft to operate at an increased aircraft MTOW limitation; which increased weight limit is equivalent to the difference between the statistical errors of LBUM computed weight to that of the actual measured aircraft weight.
A common finding when physically re-weighing an aircraft to determine the Operating Empty Weight (“OEW”) is that the weight of the empty aircraft never gets tighter, but tends to get heavier over the life of the aircraft. As aircraft age, the insulation within the cabin will retain higher amounts of moisture. Dirt will accumulate on lubricated surfaces; dirt will become embedded within the carpets and seat fabrics. Structural repairs, which consist of doubting-plates, riveted over discovered fuselage cracks, add weight to the aircraft. These weight increases will remain unrecognized for up to the 36 months interval between the aircraft 3-year re-weighing cycles. Some airlines utilize a practice of “fleet average” weighing, where a minimum of 6 aircraft plus an additional 10% of the operating fleet; i.e.: 56 of a 500 aircraft fleet will be physically re-weighed, where the remaining 444 aircraft will be assumed to have an identical averaged fleet-weight.
The scales used to determine the aircraft OEW are not required to maintain any FAA stipulated accuracy tolerance, other than an FAA requirement that the airline should calibrate the scale according to a scale calibration procedure approved by the scale manufacturer. Errors can often be as high as 0.5%.
To this point, the focus of this new invention has examined the aircraft MTOW limitation. MTOW is one of four aircraft weight limitations that are established in the flight's load planning process for a particular aircraft dispatch, as part of determining a specific aircraft weight limitation using the LBUM process of determining aircraft weight.
The methods described herein are applicable as procedures and practices used to obtain Regulatory Authority approval to amend existing aircraft weight calculation practices for determining other aircraft operating weights including: MRampW, MLW and MZFW. In today's airline operations, other aircraft weight determinations such as: MRampW, MLW and MZFW are all determined using the same foundations of the MTOW, as determined by LBUM computations.
The Maximum Ramp Weight (“MRampW”) is the MTOW plus the weight of the fuel needed to operate the engines while the aircraft taxi along the airport's service ramps, prior to take-off.
The Maximum Landing Weight (“MLW”) is maximum allowable weight at which the aircraft can “plan” to land. The MLW is the MTOW less the amount of weight associated the “planned” fuel consumption for the flight.
The Maximum Zero Fuel Weight (“MZFW”) is the maximum amount of weight less any onboard fuel. The MZFW is used to determine limits as to passengers and payload, which are loaded onto an aircraft. MZFW is the MTOW less the amount of fuel within the aircraft's fuel tanks as measured by the aircraft cockpit fuel indicators.
The Boeing 737-800 is one of the most common commercial aircraft flown worldwide by today's airlines and shall be used as the example aircraft throughout the examples and illustrations in this invention.